How Much of that part number is important?

Part numbers are incredibly important, but can also be incredibly annoying and confusing. Obviously, we all need them, but it would be nice if there were some semblance of a standard. Well, there are some standards, like capacitor grades and IC packages, but even those aren't always standard.

In to the mix, go manufacturer part number, distributor part number, and many OEMs have their own part numbering scheme. Here's an example of some extremes:

Part number: 103

Part number: GRM155R61C104KA88D

The first example is battery holder for a coin cell, and the second is a surface mount capacitor. Granted, there are a lot more options in the capacitor world, but that much of a difference is just goofy.

With the coin cell holder, it should be clear that all THREE digits are important. This particular part is a plastic and metal thru-hole battery holder for a 20 mm cell, from Keystone. I think they just number their parts in sequence, occasionally hanging on an alpha suffix.

The second example, a capacitor, is a bit different. The specific characteristics of the part are encoded in the part number. Here's part of a page from the Murata datasheet for this component.

In the case of our part number, GRM155R61C104KA88D:

GR, followed by M = General purpose products15 gives the dimensions = 1.0x0.5 mm, which is an 0402 size part5, following the 15, is the height = 0.5mmR6 represents the temperature characteristics = X5R (X5R is an EIA temperature standard code)1C covers the DC voltage, 16 volts, in this case104 is the capacitance in pico farads = 100000pf (1 and 0 are the value, 4 is the number of zeros)K is tolerance = 10%A88 represents an "individual specification code" The datasheet doesn't give any more information on what that would be except that, if it starts with E, it would represent the part's ESR.D finally, the last character, D covers the packaging. D = 180mm paper tape.

So, in this case too, every character matters.

One thing the manufacturers part number doesn't cover, but the distributor (DigiKey, in this example) often does cover is whether this would come in a full-reel, partial reel, or cut strip. The DigiKey part number for this capacitor is:

490-5415-1-ND, for cut-tape490-5415-2-ND, for a full reel490-5415-6-ND, for a Digi-reel

I don't know what happened to -3, -4, and -5.

In cases, like ICs, the manufacturer part number will specify trays, tubes, or tape and reel. For example, the 28 pin QFN version of the PIC18F2221 microcontroller.

PIC18F2221-I/ML comes in a tubePIC18F2221T-I/ML comes in tape and reel

In the case of the capacitor and microcontroller, we could probably figure out the exact part without the manufacturer. That many digits is likely to be unique. In the case of the Keystone battery clip, we most likely couldn't figure out without the name Keystone attached to it. But, even in the case of the capacitor and microcontroller, the manufacturer name is an important safety check, and will speed things up.

David K has a good point. It would be nice to get some guidance from Screaming Circuits in regards how to handle this aspect of the part number. Figuring out what part you have on hand, or can get the easiest at the lowest cost, which will work, is the art/experience we rely on you (Screaming Circuits) to determine, so we get our PCBA which works as we designed ASAP, and is the lowest cost to both parties. Perhaps another newsletter will be forthcoming soon, that addresses this?

In the case of the capacitor you say, "So, in this case too, every character matters" but that's not true. The problem I have with specifying parts is that last letter, 'D'. As an engineer I couldn't care less if the parts show up on 180mm paper tape, a 330mm plastic tape or a 26" radial tire. I just want my capacitor to meet the other specifications. Same for the IC example.

I've had production builds delayed because purchasing couldn't get the paper tape packaging when the exact same parts were available on plastic tape. I've also seen where they continued to buy bulk parts because that is what I had to specify on my prototype BOM, even though tape and reel parts were available at lower cost.

I have yet to work at a place where we could give multiple part numbers in the inventory system that were identical. It causes extra work when manufacturing has to stop while purchasing asks engineering for an alternate part number of an otherwise identical part.